Microorganisms which accumulate polyester comprising (R)-3-hydroxybutyrate units (included in the (R)-3HA unit constituting the polymer of the present invention) in the microbial cells are known (see P. A. Holmes, Phys. Technol., Vol. 16, p. 32 (1985)). This polymer has biodegradability, i.e., enzymatic decomposability, hydrolyzability, and bioaffinity, and is now attracting attention as a new type of functional material (see Yoshiharu Doi, Seibunkaisei Kobunshi Zairyo, page 19, Kogyo Chosakai (1990)). However, biological synthesis of a polymer utilizing a microorganism or an enzymatic reaction requires complicated steps such as separation of the polymer from microbial cells.
On the other hand, ring-open polymerization of D-(+)-methyl-.beta.-propiolactone is reported in Polymer Letters, Vol. 9, p. 173 (1970). However, a convenient process for synthesizing D-(+)-methyl-.beta.-propiolactone to be ring-open polymerized has not yet been established.
In addition, either of these known techniques involves various industrial problems, such as the high production cost incurred.